Contribution of sorghum to productivity of small-holder irrigation schemes: On-farm research in the Senegal River Valley, Mauritania

In Mauritania, most irrigated land was designed for, and remains devoted to, rice (Oryza sativa L.) cultivation. Decades after introduction, however, yield remains below expectations, irrigated land is gradually being abandoned, and now crop diversification is promoted to improve sustainability of irrigated agriculture. This paper presents evidence of the potential, and limitations, of sorghum (Sorghum bicolor L. Moench) cropping in small-holder irrigation schemes along the Mauritanian side of the Senegal River Valley. Results are based on 3-years of on-farm participatory research (2007–2009) carried out at five irrigation schemes in collaboration with farmers and national research and extension services. Grain yield, water productivity and gross margin of sorghum and rice were compared at plot level. Global average grain yield over years and schemes was 2.5tha−1 for sorghum, ranging from 1.7tha−1 to 3.2tha−1, compared to 5.6tha−1 for rice, ranging from 4.0tha−1 to 7.3tha−1, even though both crops had similar total above-ground biomass at maturity. Sorghum required less irrigation water than rice (435 vs. 601mm) but the smaller yield resulted in similar irrigation water productivity (0.87 vs. 0.96kgm−3) and fuel (pumping) productivity (1.71 vs. 1.93kgMJ−1). Despite smaller yields, however, sorghum profitability was significantly greater than rice (1172 vs. 788 € ha−1), due to higher market price and, in the case of one scheme, lower irrigation costs. Main constraints identified in sorghum cropping were (i) poor crop establishment because of late sowing and water logging; (ii) neglected weed management; and (iii) mismatch between irrigation delivery schedules and water requirements. The causes of these constraints are particularities of rice production systems (design and heavy soil) and farmers’ habits acquired with traditional rainfed sorghum cropping during the wet season.